1. Field of the Invention
The present invention relates to a power supply apparatus for superimposing a direct current voltage on an alternating current voltage and outputting a resulting voltage, and an image forming apparatus provided with the same.
2. Description of the Related Art
As described in Japanese Patent Laid-Open No. 2004-37642, an electrophotographic developing apparatus applies a developing voltage generated by superimposing a direct current voltage on an alternating current voltage to a developing roller, so that toner efficiently adheres to an electrostatic latent image on a photosensitive member. The toner performs reciprocal motion between the photosensitive member and the developing roller due to the alternating current voltage. Accordingly, the toner adheres to the electrostatic latent image, and toner adhered to the other portions is drawn back to the developing roller. The direct current voltage controls the amount of the toner that flies to the photosensitive member, so as to adjust the density of the image.
Incidentally, when the atmospheric temperature or humidity of an image forming apparatus changes, a photosensitive member deteriorates or the like, image density fluctuates. Therefore, it is necessary to adjust a direct current voltage that constitutes a developing potential and control the image density to be a desired density. In order to widen the adjustment range of the image density, the adjustment range of the direct current voltage must be widened.